.

"There's damage definitely done on this," said Jim Kessler, vice president for policy at Third Way, a center-left think tank.

Romney discussed his Medicare reform plan on a fall visit to Miami, according to a campaign official, but has spent much of the past week criticizing Gingrich and Obama.

Romney faces another challenge among conservatives, as the health reform he signed into law as Massachusetts governor bears many similarities to the law Obama signed several years later. As a presidential candidate, Romney has said that health reform should be handled by states, not the federal government.

Gingrich, too, has until recently backed the idea that individuals should be required to buy health insurance, a central element of Obama's plan. (For coverage of the 2012 Republican campaign, ) (Editing by Marilyn W. Thompson and Doina Chiacu)